# Observation and modeling of interspecies ion separation in inertial confinement fusion implosions via imaging x-ray spectroscopy

## TL;DR

This paper presents the first direct experimental evidence of interspecies ion separation in inertial confinement fusion implosions, using advanced x-ray spectroscopy techniques and modeling to analyze Ar concentration variations during the implosion process.

## Contribution

It provides novel experimental data and modeling validation for interspecies ion thermo-diffusion in ICF, highlighting the impact of ion separation on implosion dynamics.

## Key findings

- Detection of Ar concentration enhancement and depletion during implosion
- Agreement between experimental Ar profiles and radiation-hydrodynamic simulations
- Observation of ion separation effects near shock convergence and rebound

## Abstract

We report first direct experimental evidence of interspecies ion separation in direct-drive ICF experiments performed at the OMEGA laser facility via spectrally, temporally and spatially resolved imaging x-ray-spectroscopy data [S. C. Hsu et al., EPL 115, 65001 (2016)]. These experiments were designed based on the expectation that interspecies ion thermo-diffusion would be strongest for species with large mass and charge difference. The targets were spherical plastic shells filled with D2 and a trace amount of Ar (0.1% or 1% by atom). Ar K-shell spectral features were observed primarily between the time of first-shock convergence and slightly before neutron bang time, using a time- and space-integrated spectrometer, a streaked crystal spectrometer, and two gated multi-monochromatic x-ray imagers fielded along quasi-orthogonal lines of sight. Detailed spectroscopic analyses of spatially resolved Ar K-shell lines reveal deviation from the initial 1% Ar gas fill and show both Ar-concentration enhancement and depletion at different times and radial positions of the implosion. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree reasonably with calculated profiles associated with the incoming and rebounding first shock.